The present invention relates generally to gas turbine engines, and, more specifically, to rotor bearings therein.
In a gas turbine engine, air is pressurized in a compressor and mixed with fuel in a combustor for generating hot combustion gases. The hot gases flow downstream through turbine stages which extract energy therefrom. A high pressure turbine is joined to the compressor by a rotor shaft. Another rotor shaft joins a low pressure turbine to a fan disposed upstream from the compressor in an exemplary turbofan gas turbine aircraft engine application.
The two rotor shafts are mounted in suitable bearings supported in corresponding stator frames of the engine. Each bearing has a corresponding bearing housing through which lubricating oil is suitably channeled during operation.
One bearing supporting the high pressure turbine rotor shaft may be located in the center bore of the engine inside the surrounding annular combustor. The heat generated by the combustor during operation also heats the adjacent bearing housing and subjects the bearing housing to thermally induced stress during operation. Such thermal stresses increase as the differential temperature between hot and cooler housing components increase, especially where adjacent components restrain such thermal expansion therebetween.
The bearing housing may be protected in a conventional manner by using a surrounding thermal shield between it and the hot combustor, and by channeling bleed air from the compressor to provide a thermal air barrier between the combustor and the bearing housing. This increases the complexity of the bearing housing in this location, and in relatively small gas turbine engines, the ability to introduce such features in the bearing housing is limited by the small available space.
In one conventional configuration, the bearing housing includes an inner structural shell in which the bearing is mounted, with opposite axial ends of the inner shell being sealed to the rotor shaft. Various service tubes or lines carry lubricating oil to and from the inner shell, as well as providing air ventilation thereof.
The inner shell may be surrounded by an outer shell which is pressurized using air bled from the compressor for preventing leakage of the lubricating oil from the inner shell. And, the air inside the outer shell provides a thermal barrier for the inner shell.
The service lines must extend through the outer shell, and therefore require suitable seals therewith. In one conventional configuration, the service lines may be rigidly interconnected with the outer and inner shells to provide a suitable solid metal seal therebetween in the local vicinity of the corresponding service lines. However, the outer shell will operate at a greater temperature than the inner shell due to the hot combustion environment surrounding the outer shell. The inter-shell plenum is pressurized with cooler bleed air and operates at a correspondingly lower temperature. And, the oil within the inner shell is substantially cooler yet.
Accordingly, the outer shell will thermally expand both radially and axially relative to the inner shell with physical constraints therebetween created by the local rigid joints at the respective service lines. Those joints are therefore subject to thermal stresses during operation which may be substantial for certain engine configurations, and may lead to a shortened useful life of the bearing housing.
Accordingly, it is desired to provide an improved bearing housing subject to combustor heating having reduced thermal stress therein.
A bearing housing includes inner and outer shells through which a rotor shaft may extend. A service tube is fixedly joined to the inner shell and extends through a service aperture in the outer shell. A flexible coupling sealingly joins the service tube to the outer shell at the service aperture for permitting differential thermal movement between the inner and outer shells at the service tube.